When stripped screws — or screws where the slots in the screw's head have worn away — leave screwdrivers with little scope to work, duct tape can help provide that missing grip.
To remove such a screw, attach a piece of duct tape to the top of the screw, adhesive side down. Then, using a screwdriver, press firmly into the head of the screw and turn slowly.
You want to keep consistent, even pressure when turning the screw. However, be sure to use a hand screwdriver, as a power drill or driver will not work well because of the torque.
The duct tape provides the stripped screwdriver with something to hold onto. Note that a screwdriver larger than the screw head opening might help it connect and grab on better.